Rosetta: Target in Sight

by Paul Gilster on March 28, 2014

The European Space Agency’s Rosetta spacecraft, having traveled for ten years, is on track for its close-up investigation of comet 67P/Churyumov–Gerasimenko to begin later this year. Three years ago we had the first actual image of the comet, a 13-hour exposure taken shortly before the craft entered a lengthy period of hibernation. On the 20th of January, Rosetta was ‘awakened’ and controllers are in the process of commissioning its onboard instruments. As part of the process, we have two ‘first-light’ images taken on March 20 and 21.

We’re seeing Rosetta from a distance of 5 million kilometers, from which vantage we see its light in less than a pixel through a series of 60 to 300 second exposures. Even so, the sense of exhilaration in the words of OSIRIS principal investigator Holger Sierks (Max-Planck-Institut für Sonnensystemforschung, Göttingen) is palpable:

“Finally seeing our target after a 10 year journey through space is an incredible feeling. These first images taken from such a huge distance show us that OSIRIS is ready for the upcoming adventure.”

Keep in mind the relevance of Rosetta’s mission not only to the evolution of the Solar System but also to future propulsion ideas. One area of interest is the interaction between the solar wind and cometary gases, needed information as we deepen our knowledge not only of the solar wind itself but how its stream of charged particles might be used in electric and magnetic sail concepts. The solar wind’s variability is one key issue about which we have much to learn.

Rosetta’s studies will be wide-ranging. The spacecraft flies with eleven science instruments onboard, fine-tuned to study everything from the comet’s surface geology to its internal structure and the dust and plasma that surround it. OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) has both a wide-angle and a narrow-angle camera involved in the capture of the early images, all part of six weeks of activity as all eleven instruments are checked out for arrival in August.

This ESA news release offers more, noting that on its current trajectory, the spacecraft would pass approximately 50,000 kilometers from the comet at a speed of 800 meters per second. It will be in May that a series of maneuvers are begun to reduce Rosetta’s velocity relative to the comet to 1 meter per second, with the aim of bringing it within 100 kilometers by the first week of August. The re-activation of OSIRIS now gives way to checks on the other instruments as we prepare for what ought to be a memorable encounter. The Philae lander is scheduled to attempt its landing in November.

One area of interest is the interaction between the solar wind and cometary gases, needed information as we deepen our knowledge not only of the solar wind itself but how its stream of charged particles might be used in electric and magnetic sail concepts.

I don’t understand why we need to do these measurements so far away. Wouldn’t a satellite anywhere outside of the Earth’s magnetic field be sufficient, e.g. in cis-lunar space, or better yet, in the same orbit as Earth, but trailing or leading us?

Months after reawakening from a record-setting slumber, NASA has announced that three of its instruments aboard Rosetta, the European Space Agency’s (ESA) comet-hunting spacecraft, have started sending data back to Earth.

Rosetta is primed to become the first spacecraft to orbit a comet (67P/Churyumov-Gerasimenko) in August, and will also deploy a lander, Philae, to the comet’s nucleus in November. During its unprecedented mission, it is hoped that Philae will drill into the nucleus, providing a glimpse – for the first time ever – into a comet’s composition.

The three NASA instruments are the Microwave Instrument for Rosetta (MIRO), Alice (an ultraviolet spectrometer), and the Ion and Electron Sensor (IES). MIRO will provide data about the evolution of the comet’s tail and “coma” (the area around the comet’s nucleus), shedding light upon how this section of the comet develops as it approaches and departs our nearest star, the Sun.

Alice will analyze the gases within the coma, and the comet’s production of water, carbon dioxide, and carbon monoxide. It is hoped – along with Philae’s surface analyses – that Alice’s data will aid scientists in determining the nucleus’ composition.

An image snapped earlier this month by ESA’s Rosetta spacecraft shows its target comet has quietened, demonstrating the unpredictable nature of these enigmatic objects.

The picture was captured on 4 June by Rosetta’s scientific camera, and is the most recent full-resolution image from the narrow-angle sensor. It has been used to help fine-tune Rosetta’s navigation towards comet 67P/Churyumov–Gerasimenko, which was 430 000 km away at the time.

Strikingly, there is no longer any sign of the extended dust cloud that was seen developing around nucleus at the end of April and into May, as shown in our last image release. Indeed, monitoring of the comet has shown a significant drop in its brightness since then.

“The comet is now almost within our reach – and teaching us to expect the unexpected,” says the camera’s Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research in Germany.

“After its onset of activity at the end April, our images are currently showing a comet back at rest.”

I’m just back from vacation and struggling to catch up but I could not wait to post these amazing new images of comet Churymov-Gerasimenko from Rosetta. The nucleus of the comet is clearly a contact binary — two smaller (and unequally sized object) in close contact. The CNES page where this photo was released says the whole nucleus measures 4 by 3.5 kilometers, in good agreement with Hubble and Spitzer estimates. Philippe Lamy is quoted as estimating that the two components would have come into contact at a relative speed of about 3 meters per second in order to stick together in this way.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last nine years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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